Device for regulating the engine braking power of an internal combustion engine

ABSTRACT

Device for controlling the engine braking power of an internal combustion engine (1) in a motor vehicle, which is equipped with a compression braking device arranged in brake mode to open the exhaust valves at the end of the induction stroke, at the end of the compression stroke or only at the latter, and an exhaust-driven turbocompressor unit (3) with a turbine portion (30), which has variable geometry to vary the degree of charge of the compressor (8). Restrictor valve elements (42) are arranged in the exhaust conduit (41) upstream of the turbine portion (30).

CROSS REFERENCE TO RELATED APPLICATION

This is the 35 USC §371 National Stage of International applicationPCT/SE96/01712filed on Dec. 19, 1996, which designated the United Statesof America.

FIELD OF THE INVENTION

The present invention relates to a device for controlling the enginebraking effect in an internal combustion engine in a motor vehicle,which is equipped with a compression braking device, means for varyingthe degree or charge in brake mode, comprising, firstly, anexhaust-driven turbocompressor unit with a turbine portion and acompressor portion, and secondly, valve means disposed in engine exhaustconduit, and means actuatable by the driver of the vehicle foractivating the compression braking device and the means for varying thedegree charge.

BACKGROUND OF THE INVENTION

It is known that the engine braking power of a vehicle can be increasedwith the aid of a device or the above described type, by means of whichthe engine combustion chambers in brake mode during the latter portionof the compression stroke is connected to the exhaust system, forexample by opening the regular exhaust valve. The result will be thatthe air compressed during the compression stroke flows out of thecylinders and that the compression work carried out during thecompression stroke will not be recovered during the expansion stroke,and this will result in an increase in the engine braking power. Anadditional increase in the braking power can be achieved in this case ina known manner by connecting the exhaust system to the cylinders duringthe latter portion of the induction stroke, so that gas from the exhaustsystem can flow into the cylinders. This results in an increase inpressure in the cylinder and an inner charging so that the compressionwork after breaking off the communication between the cylinders and theexhaust system will be increased.

In a device known by SE-A-9401059 of the type described by way ofintroduction, said valve means are formed of an exhaust pressureregulator (EP regulator), i.e. a damper in the exhaust line downstreamof the turbine portion of the turbocompressor unit. By varying thedegree of opening of the damper, the driver can control the degree ofinner charging and thus increase or reduce the braking power. The damperis controlled by a control unit into which the driver feeds a desiredvalue of the vehicle retardation and into which engine data is fed viasensors such as the degree vehicle retardation and into which enginedata is fed via sensors such as the degree of charge and the rpm, andvehicle data such as vehicle speed, accelerator position and clutchpedal position.

SUMMARY OF THE INVENTION

The purpose of the present invention is in general to achieve a deviceof the type described by way of introduction which makes it possible toachieve higher braking power in the engine than what could be achievedwith the described device. The particular purpose is to achieve a devicein which the turbocompressor unit can be utilized in a better mannertogether with the valve means in the exhaust line to vary the brakingpower of the engine.

This is achieved according to the invention by virtue of the fact thatthe valve means are restrictor valve means arranged in the engineexhaust conduit upstream of the turbine portion of the turbocompressorunit.

By placing the valve means closer to the exhaust outlet from thecylinders, there is a reduction in the volume of the exhaust conduitbetween the exhaust valves and the valve means in the exhaust conduit,which means that the pistons will not need to exhaust as much gas aspreviously in order to create a certain counter-pressure. Highcounter-pressure can therefore be obtained more rapidly.

In a turbocharged engine with an exhaust pressure regulator downstreamof the turbine, the pressure drop required over the turbine, so that theturbine will be able to drive the compressor, cannot be obtained inbrake mode. By instead placing the restrictor valve means prior to theturbine portion and adapting the restriction area to the turbine area,the turbocompressor unit can provide supercharging even in brake mode.It is true that the pistons are imparted energy from the gas during theinduction stroke, but the work which the pistons must carry out againstthe gas during the compression stroke will be so much greater that thenet effect will be a higher braking power. Another advantage ofcirculating large volumes of gas through the engine in brake mode isthat a greater amount of heat will be removed through the gas than ininstallations with exhaust pressure regulators in which the heat isprimarily diverted by cooling water.

The turbine portion in a turbocompressor unit which is dimensioned tooperate in drive mode within the normal rpm range of the engine, will betoo large to be able to supercharge in brake mode. The device accordingto the invention is therefore regularly suited to be used inturbocharged engines with turbines which have variable geometry, or inso-called turbocompound engines which have a turbocompressor unit with afirst turbine stage, which drives the compressor portion, and a secondturbine stage, which is coupled, via a transmission, to the enginecrankshaft. In such turbo units, the first turbine stage is a smallhigh-pressure turbine, while the second turbine stage is a largerlow-pressure turbine. It has been found that the corrected mass flow tothe compressor turbine in brake mode is approximately equal to that forturbocompound engine mode. In a conventional turbocharged engine, thecompressor turbine is substantially larger, which means that thecorrected massflows in brake mode and drive mode will approximatelyequal first at engine rpm above the normal operating rpm.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail below with reference toexamples shown in the accompanying drawings, where:

FIG. 1 shows schematically a turbocompound engine with a deviceaccording to the invention,

FIG. 2 a simplified schematic representation of the engine in FIG. 1;

FIG. 3 a simplified schematic representation of a turbocharged enginewith a turbine with variable geometry and with a device according to theinvention;

FIG. 4 a schematic representation of a turbocompound engine with adevice according to the invention in a third embodiment,

FIG. 5 a simplified schematic representation of the engine in FIG. 4,

FIG. 6 a longitudinal section through an exhaust restrictor valveaccording to the invention; and

FIG. 7 a longitudinal section through a combined restrictor and ventingvalve on the intake side.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1, 1 designates a six cylinder engine with a gearbox 2 attachedthereto.

A turbocompressor unit, generally designated 3, has a first turbinestage 4 and a second turbine stage 5 connected to the engine exhaustmanifold 6. The first turbine stage 4 is a small high-pressure stage,which drives a compressor 8 connected to the engine intake conduit 7,while the second turbine stage 5 is a larger low-pressure stage which iscoupled via a transmission 9 to the engine crankshaft 10. Thetransmission 9 comprises a gear 11 on the output shaft 12 of the turbinestage 5, said shaft 12 driving, via a pair of gears 13, 14 on anintermediate shaft 15, a gear 16 on the crankshaft 10 (see FIG. 2). Viaa first continuously adjustable waste-gate valve 17, a larger or smalleramount of exhaust can be shunted past the high-pressure turbine 4 inorder to vary the degree of charge. Via a second shunt valve 18, theexhaust can be shunned past the low-pressure turbine 5. The engine 1 hasa schematically indicated compression braking device 19, which can be ofthe type which is shown and described in SE-466 320, and by means ofwhich the engine cylinders during the latter portion of inductionstroke, as well as during the latter portion of the compression stroke,can be connected to the engine exhaust manifold to increase the enginebraking power. For a more detailed description of the construction andfunction of a possible embodiment of the compression braking device 19,reference to made to SE-466 320.

FIG. 2 shows schematically a few details which are not apparent fromFIG. 1, namely: an air filter 20, a charged air cooler 21, an intakemanifold 22, intake valves 23, cylinders 24, exhaust valves 25, and amuffler 27.

FIG. 3 shows an engine installation differing from that described aboveby virtue of the fact that the turbocompound unit has been replaced by aturbocompressor unit with a turbine portion 30, which has continuouslyvariable geometry. Details corresponding to those in FIG. 2 have beengiven the same reference numerals in FIG. 3 as in FIG. 2.

FIGS. 4 and 5 show an engine installation differing from that in FIGS. 1and 2 by virtue of the fact that the waste-gate valve 17 on the exhaustside has been eliminated and been replaced by a combined restrictor andventing valve 80 in the induction conduit 7 on the pressure side of thecompressor 8. The valve 80 is shown in more detail in FIG. 7. Partscorresponding to those in FIGS. 1 and 2 have been given the samereference numerals in FIGS. 4 and 5 as in FIGS. 1 and 2.

The valve 80 has a housing 81 made in one piece with the engineinduction conduit 7 with a cylinder 82, in which a piston 83 is axiallydisplaceable. The piston has a through-bore 84 and is biased by a spring85 towards the open position shown in FIG. 7, in which air in theinduction conduit can flow through the bore 84 to the engine cylinder.When the degree of charge of the compressor 8 is to be reduced, pressuremedium is introduced to the cylinder chamber 86 to the left of thepiston 83, and the piston is thus displaced to the right in FIG. 7 sothat the piston portion 87 to the left of the bore 84 is displaced intothe induction conduit 7 and reduces its flow-through area. At the sametime, the piston portion 88 to the right of the bore 84 reveals theinlet 89 to the venting conduit 90 for releasing induction air from theinduction conduit when the valve piston is in the restriction position.A valve 80 on the induction side operates in a cleaner environment thana waste-gate valve on the exhaust side and is also subjected tosubstantially lower thermal load than the latter. The valve 80 is ofparticularly simple construction by virtue of the fact that it only hasa single moving part, i.e. the piston 83, which functions both as arestrictor in the induction conduit and as a valve element for theventing opening 89.

The manifold 6, as is most clearly illustrated in FIGS. 2 and 3, isdivided into two submanifolds 40, the output exhaust conduits 41 ofwhich meet in a confluence before the inlet to the turbocompressor unit3 resp 30. In each exhaust conduit 41 a restrictor valve 42 is disposedin accordance with the invention, each valve having a completely openposition and a restrictor position in which the flow-through area of theconduit 41 is reduced to create an exhaust counter-pressure in theexhaust manifold 6 during engine braking.

A valve 42, which is to function in the environment or an exhaustmanifold, must be able to withstand high mechanical and thermalstresses. In the open position it must not present any flow obstacles orcreate turbulence in the exhaust conduit. A valve 42 which fulfillsthese conditions is shown in FIG. 6, where 50 designates a cylindricalvalve housing, which is preferably cast in one piece with the exhaustmanifold 6. The inner cylinder chamber 51 of the housing portion 50opens into the interior of the exhaust conduit 41. The opening 52 itselfis surrounded by a conical seat 53, against which there abuts acorresponding seat 54 at an end of a sleeve 55 of stainless steel. Thesleeve 55 is kept in place by a cover 56 held securely in place on thehousing portion 50 by means of screws. The cover 56 has a conicalsurface 57 which presses against a facing conical surface at the end ofthe sleeve 55. The sleeve 55 has a portion 58 of reduced diameter sothat a cylindrical air gap 59 is formed, which communicates with thesurrounding air via an annular gap 66 between the housing portion 50 andthe cover 56.

Inside the sleeve 55 there is a valve element in the form of a hollowpiston 60. As can be seen in FIG. 6, there is a small play "S" betweenthe exterior lateral surface of the piston 60 and the interior lateralsurface of the sleeve 55. The cylindrical portion of the piston 60consists of a tube 60a of hard-chromium plated stainless steel. Endplates 61, 62 are fixed to the ends of the tube 60a. These from valvediscs with conical edge portions 61a, 62a and are preferably sintered.The sleeve 55 is provided at its distal end with a seat 55a, againstwhich the edge portion 61a of the disc 61 is in sealing contact when thevalve is in its open position (as is shown in FIG. 4). When compressedair with a pressure on the order of 8 bar is supplied to the cylinderchamber 63 via an inlet 64, the piston 60 is displaced to the left inFIG. 4 at the same time as leaking air into the gap "S" blows it free ofany soot there. The piston 60 is displaced perpendicular to the exhaustconduit 41 and stops with its disc 61 at a small distance from a surface65 of the opposite wall portion of the conduit 41, when the conical edgeportion 62a of the disc 62 strikes an inner conical seat 55b of thesleeve 55, so that exhaust cannot leak into the cylinder chamber. Aslong as there is pressure in the cylinder chamber, the piston 60 is heldin its restricting position. The diameter of the piston 60 and thecross-section of the conduit 41 are adapted to each other so that arestricted passage for exhaust is obtained between the inner wall of theconduit and the piston. When the piston 60 is to be returned to itsstarting position in FIG. 6, the cylinder chamber 63 is drained, and theexhaust pressure, which is propagated through the gap "S" and actingagainst the disc edge 62a, causes the piston to be displaced into thesleeve 55. No return spring is required and the only moving part of thevalve is the piston 60, and this results in high operationalreliability.

The compression braking device 19 is electrically operated while thevalves 17, 18, 42 and 70 are operated by compressed air. They arecontrolled by a control valve unit 70 connected to a pressure source(not shown) and a control unit 71, which is preferably a microprocessor,which provides output signals for turning the compression braking deviceon and off and for adjusting the valves 17, 18 and 42 depending on anumber of different engine and vehicle variables fed into the controlunit from sensors which are known per se and are not shown in moredetail here. As is indicated in FIG. 1. signals are fed into the controlunit 71 representing induction air pressure (charge pressure) and enginerpm, i.e. engine data, and signals representing ABS on/off, vehiclespeed, clutch pedal position, accelerator position, cruise controlon/off and retardation level, i.e. vehicle data.

The device can function in the following manner:

The driver adjusts, with a hand control (not shown) the retardation to acertain level and activates the cruise control, so that a signalrepresenting the selected retardation is fed into the control unit 71,which compares the set desired value of the retardation with the actualvalue of the retardation computed via the actual value of the speed.When the driver lets up on the accelerator, providing the clutch pedalis not depressed, the control unit 71 will set, via the control valveunit 70, the restrictor valves 42 in restrictor position, open the shuntvalve 18 to bypass the second turbine stage 5 and, depending on thedifference between the actual value and the desired value, adjust thewaste-gate valve 17 to provide a suitable degree of charge in the firstturbine stage 4, and activate the compression braking device 19. In theembodiment shown in FIG. 3, the degree of charge is instead provided byvarying the turbine geometry in the turbine portion 30. If the selectedlevel of retardation should be too high in view of the road surface, sothat the drive wheels lose their grip, the ABS system reduces the enginebraking power by sending a signal to turn off the compression brake 19and then engage it again at a lower retardation level, or,alternatively, to provide the driver with the possibility of selecting alower retardation level. Disengagement of the compression brake 19 alsooccurs if the driver should depress the clutch pedal, which is importantto prevent killing the engine and thereby losing power steering andpower brakes.

What is claimed is:
 1. Apparatus for controlling the engine brakingeffect in an internal combustion engine in a motor vehicle, which isequipped with a compression braking device, the apparatuscomprising:means for varying the degree of charge in brake mode, whichcomprise: a) an exhaust-driven turbocompressor unit with a turbineportion and a compressor portion, and b) a restrictor valve disposed inan engine exhaust conduit upstream of the turbine portion of theturbocompressor unit; means actuatable by a driver of the vehicle foractivating the compression braking device and the means for varying thedegree of charge; and a combined restrictor and venting valve unitarranged in an engine induction conduit on the pressure side of thecompressor portion.
 2. The apparatus according to claim 1, wherein theturbocompressor unit is coordinated with a first wastegate valve whichcan be set for various charge pressure levels.
 3. The apparatusaccording to claim 2, wherein the turbocompressor unit comprises a firstturbine stage, which drives the compressor portion and is coordinatedwith the first wastegate valve; and a second turbine stage which iscoupled, via a transmission, to an engine crankshaft and is coordinatedwith a second wastegate valve, which in one position conducts exhaustpast the second turbine stage.
 4. The apparatus according to claim 1,wherein the turbocompressor unit has a turbine portion with variablegeometry.
 5. The apparatus according to claim 1, wherein the restrictivevalve has a restrictor position and a completely opened position. 6.Apparatus for controlling the engine braking effect in an internalcombustion engine in a motor vehicle, which is equipped with acompression braking device, the apparatus comprising:means for varyingthe degree of charge in brake mode, which comprise: a) an exhaust-driventurbocompressor unit with a turbine portion and a compressor portion,and b) a restrictor valve disposed in an engine exhaust conduit upstreamof the turbine portion of the turbocompressor unit; means actuatable bya driver of the vehicle for activating the compression braking deviceand the means for varying the degree of charge; said restrictor valvecomprising at least one valve having a cylinder communicating with theengine exhaust conduit and arranged perpendicularly to said exhaustconduit, said cylinder receiving with radial play a valve element in theform of a piston displaceable into the exhaust conduit under theinfluence of a pressure medium, said piston having a distal end surfaceand a proximal end surface and a valve disc at each end surface; andwherein the valve disc at the proximal end surface, in an extendedposition of the piston, abuts against a proximal seat in the cylinder toform a restricted exhaust passage past the piston; and the valve disc atthe distal end surface, in a retracted position of the piston, contactsa distal seat in the cylinder.
 7. The apparatus according to claim 6,wherein the cylinder is a sleeve of stainless steel which is receivedwith play in a cylindrical space in a valve housing cast in one piecewith a manifold.
 8. The apparatus according to claim 6, wherein thevalve piston consists of a tube of hard chromium-plated stainless steeland a sintered valve disc with a conical edge surface fixed at eitherend of the tube.
 9. The apparatus according to claim 6, for use in asix-cylinder engine with two exhaust manifolds for each three cylinders,wherein a restrictor valve is arranged in each manifold.
 10. Theapparatus according to claim 6, wherein the turbocompressor unit iscoordinated with a first wastegate valve which can be set for variouscharge pressure levels.
 11. The apparatus according to claim 10, whereinthe turbocompressor unit comprises a first turbine stage, which drivesthe compressor portion and is coordinated with the first wastegatevalve; and a second turbine stage which is coupled, via a transmission,to an engine crankshaft and is coordinated with a second wastegatevalve, which in one position conducts exhaust past the second turbinestage.
 12. The apparatus according to claim 6, wherein theturbocompressor unit has a turbine portion with variable geometry. 13.The apparatus according to claim 6, wherein a combined restrictor andventing valve unit is arranged in an engine induction conduit on thepressure side of the compress or portion.